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Protein
Proteins are part of every cell, tissue, and organ in our bodies. These body proteins are
constantly being broken down and replaced. The protein in the foods we eat is digested into
amino acids that are later used to replace these proteins in our bodies.
There are many different proteins in your body, and they perform different functions.
Proteins functions include:
Contributing to enzyme activity that promotes chemical reactions in the body
Signaling cells what to do and when to do it
Transporting substances around the body
Keeping fluids and pH balanced in the body
Serving as building blocks for hormone production
Helping blood clot
Promoting antibody activity that controls immune and allergy functions
Serving as structural components that give our body parts their shapes
Protein is found in the following foods:
meats, poultry, and fish
legumes (dry beans and peas)
tofu
eggs
nuts and seeds
milk and milk products
grains, some vegetables, and some fruits (provide only small amounts of protein
relative to other sources)
As we mentioned, most adults in the United States get more than enough protein to meet
their needs. It's rare for someone who is healthy and eating a varied diet to not get enough
protein.
What are the types of protein?
Proteins are made up of amino acids. Think of amino acids as the building blocks. There are
20 different amino acids that join together to make all types of protein. Some of these
amino acids can't be made by our bodies, so these are known as essential amino acids. It's
essential that our diet provide these.
In the diet, protein sources are labeled according to how many of the essential amino acids
they provide:
A complete protein source is one that provides all of the essential amino acids. You
may also hear these sources called high quality proteins. Animal-based foods; for
example, meat, poultry, fish, milk, eggs, and cheese are considered complete protein
sources.
An incomplete protein source is one that is low in one or more of the essential amino
acids. Complementary proteins are two or more incomplete protein sources that
together provide adequate amounts of all the essential amino acids.
For example, rice contains low amounts of certain essential amino acids; however, these
same essential amino acids are found in greater amounts in dry beans. Similarly, dry beans
contain lower amounts of other essential amino acids that can be found in larger amounts in
rice. Together, these two foods can provide adequate amounts of all the essential amino
acids the body needs.
Quick Q& A
Is it true that complementary proteins must be eaten together to count as a
complete protein source?
In the past, it was thought that these complementary proteins needed to be eaten at the
same meal for your body to use them together. Now studies show that your body can
combine complementary proteins that are eaten within the same day. 1
How much protein do I need?
Maybe you've wondered how much protein you need each day. In general, it's
recommended that 10–35% of your daily calories come from protein.
Here are examples of amounts of protein in food:
1 cup of milk has 8 grams of protein
A 3-ounce piece of meat has about 21 grams of protein
1 cup of dry beans has about 16 grams of protein
An 8-ounce container of yogurt has about 11 grams of protein
Added together, just these four sources would meet the protein needs of an adult male (56
grams). This doesn't count all the other foods that add smaller amounts of protein to his
diet.
Rather than just focusing on your protein needs, choose an overall healthy eating plan that
provides the protein you need as well as other nutrients.
To help you make lower-fat protein choices —
Choose meats that are leaner cuts and trim away any fat you can see. For chicken
and turkey, remove the skin to reduce fat.
Substitute pinto or black beans for meat in chili and tacos.
Choose low-fat or fat-free milk and yogurt.
Choose low-fat or fat-free cheese.
Choose egg whites or pasteurized egg white products.